Heretofore, hindered phenol-based compounds are useful as a polymerization inhibitor, an antioxidant, a thermal stabilizer, or the like, and various derivatives thereof are proposed. In particular, for use as a polymerization inhibitor, a hindered phenol-based polymerization inhibitor is widely used as an inhibitor for controlling non-preferred polymerization reactions at the time of storing monomers for a long time or synthesizing and/or purifying monomers. As examples of the aforementioned hindered phenol-based polymerization inhibitors, mention may be made of, for example, 2,6-di-t-butyl-p-cresol, 2,6-di-t-butyl-4-dimethylaminomethylphenol, and the like, as described in Patent Documents 1 to 6 shown below.